Method for manufacture of rectilinear guide unit

ABSTRACT

The present invention relates to a method of manufacture of a slider of a rectilinear guide unit for guiding a movable body such as a work table of a machine tool, an industrial robot or the like by moving along an orbital rail arranged on a stationary section such as a bed, column or the like as it bears a load thereon. This method comprises a first step in which a metallic block main body as a core of the slider is machined to a predetermined shape and to form ball load rolling contact surfaces in the block main body and a second step in which the block main body machined in the previous step is inserted into a mold so as to allow a die-molding material to be padded thereon to thereby form an endless ball circulation path wherein in the first step, chamfered sections are formed on the corners of the block main body corresponding to a portion where the above-mentioned endless ball circulation path is formed.

TECHNICAL FIELD

The present invention relates to a method of manufacture of a slider fora rectilinear guide unit for guiding a movable body such as a work tableof a machine tool, an industrial robot and etc. while moving along anorbital rail arranged on a bed, column or the like, and moreparticularly to an improvement in a method in which a slider is formedby padding a die-molding material such as a synthetic resin to ametallic block main body.

BACKGROUND TECHNOLOGY

Conventionally, as a linear guide unit of the above type, there is knownthe one that has a structure comprising a orbital rail arranged on astationary portion such as a bed and having ball rolling contactsurfaces and a slider fastened to the orbital rail through a number ofballs and movable along the rail which supports a movable body such as atable.

Further, the slider comprises a mobile block having ball load rollingcontact surfaces opposing to the ball rolling contact surface of theorbital rail through the balls and ball return holes parallel to theball load rolling contact surfaces and capable of moving along theorbital rail following the rolling of the balls, a pair of covers havingchange-direction paths for establishing communication between the ballload rolling contact surfaces and the ball return holes and ballretainers attached to the mobile block so as to prevent the falling ofthe balls from the ball load rolling contact surfaces and the endportions of the ball return holes are connected by the change-directionpath when the covers are fixed to the front and rear end surfaces of themobile block, respectively, thereby completing an endless circulationpath for the balls in the slider.

In the case of the slider of the conventional rectilinear guide unit ofthe above-described structure, the process of drilling the ball returnholes and the fixing of the ball retainers to the mobile block becomesnecessary resulting in taking much time and labor for its manufacture sothat the present applicant proposed a method of manufacture of theslider by making use of extrusion molding of a synthetic resin (refer toJapanese Unexamined Patent Publication No. 317762/1995).

More concretely, the above-proposed method is such that a syntheticresin is padded onto the metallic block main body having theabove-mentioned load rolling contact surfaces subjected to cutting sothat the ball return holes and the ball retainers are molded integralwith the block main body and the ball guide sections on the side of theinner peripheral surface of each of the change-direction paths whichhave hitherto been formed in the covers are also molded on the endsurfaces of the block main body to thereby manufacture the movableblock. Besides the advantage of being able to manufacture a mobile blockof a complicated shape in a simple manner, this proposed method has alsosuch advantage that an endless ball circulation path provided with ballreturn holes, inner peripheral side ball guide sections and ballretainers formed continuous with one another can be formed with asynthetic resin thereby smoothing the circulation of the balls.

Now, where such endless ball circulation path is continuously formedwith the synthetic resin, it is usual that the molten resin immediatelyafter injection-molding solidifies as it contracts toward a directionparallel to the ball return holes but since such endless circulationpath itself is so formed as to surround the block main body, in the caseof the mobile block which has been subjected to molding, the syntheticresin forming the endless ball circulation path binds the block mainbody tightly and a tensile stress remains in the molded synthetic resin.Consequently, there has arisen the problem that when the block main bodyhas front and rear corners near the boundary of the ball return holesand the inner peripheral side ball guide sections formed of thesynthetic resin, the tensile stress concentrates on the corners causingthe synthetic resin to crack thereby hindering the smooth rolling of theballs in the endless ball circulation path.

Further, there has also been the problem that when the block main bodyhas corners formed of synthetic resin, the flow of the molten resin ishindered at the time of injection-molding and the fluidity of suchmolten synthetic resin becomes insufficient so that a weld line isgenerated in the synthetic resin forming the endless ball circulationpath and the smooth rolling of the balls is hindered because of thepresence of such weld line.

In addition, due to the fact that when the block main body has cornersformed of synthetic resin, the flow of the molten resin is hindered dueto the presence of these corners, the thickness of the synthetic resinat the ball return holes and the ball retaining sections tends to becomenon-uniform and it has not been able to avoid the generation ofdeformation of the ball return holes and the ball retaining sections inthe cooling process after molding. Accordingly, there has been theproblem that the smooth rolling of the balls is hindered because of thispoint, too.

Now, in order to allow the balls rolling in the endless ball circulationpath to circulate smoothly along a predetermined track, it is necessaryto prevent each of the balls rolling within the endless ball circulationpath from unsteadily moving right and left by reducing the gap betweenthe ball and the inner wall of the endless circulation path to aminimum. Accordingly, in order to secure the smooth movement of theslider with respect to the orbital rail, it is necessary to mold theendless ball circulation path to a predetermined dimensional accuracywithout fail so that a special consideration has been required forpadding a synthetic resin to the metallic block main body byinjection-molding.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the above-describedproblems and an object of the invention is to provide a method ofmanufacture of a slider of a rectilinear guide unit in which when theslider of the rectilinear guide unit provided with ball return holes andball retaining sections formed by padding a synthetic resin on ametallic block main body, no cracking generates in the synthetic resinforming an endless ball circulation path and ball return holes and ballretaining sections can be accurately formed.

In order to achieve the above-described object, a method of manufactureof a slider of a rectilinear guide unit according to the presentinvention comprises a first step in which a metallic block main body asa core of the slider is machined to a predetermined shape and ball loadrolling contact surfaces are formed in the block main body and a secondstep in which the block main body formed in the first step is insertedinto a mold to thereby mold a die-molding material to form an endlessball circulation path and characterized in that the first step includesforming chamfered sections at corners of the block main body atpositions corresponding to the portion where the endless ballcirculation path is formed.

According to the method of the present invention comprising theabove-mentioned steps, since the first step includes the formation ofthe chamfered sections on the corners of the block main body atpositions corresponding to the portion where the endless ballcirculation path is formed, even when the die-molding material is paddedto the block main body so as to surround the latter, the die-moldingmaterial forming the endless ball circulation path does not crack due toa tensile stress applied on the die-molding material after completion ofmolding to thereby secure the smoothness of rolling of the balls in theendless ball circulation path.

Further, by the formation of the chamfered sections on the corners ofthe block main body at a position corresponding to the endless ballcirculation path, the molten die-molding material injected into the moldquickly spreads in the longitudinal direction of the block main body sothat the thickness of the ball return holes and the ball retainingsections forming parts of the endless ball circulation path can beequalized with ease, the generation of deformation or distortion ofthese portions after the completion of molding can be controlled and theformation of a welding line of the die-molding material such as asynthetic resin in the endless ball circulation path can be prevented.Accordingly, it is possible to secure the smooth rolling of the ballswithin the endless ball circulation path from this point, too.

In the above case, the chamfered sections to be formed at the corners ofthe block main body may be planar or curved.

Further, according to the method of the present invention, when themolten die-molding material is injected into the mold in the secondstep, it is preferable that the molten die-molding material be injectedfrom a direction parallel to the load rolling contact surface of theblock main body because by so doing, the flow velocity of the moltendie-molding material in the longitudinal direction of the block mainbody is improved to form the ball return holes and the ball retainingsections more accurately thereby smoothing the rolling of the balls.

It should be noted that in the inventions described in claims 1 through3, whether or not the die-molding material is padded to the block mainbody to form ball retainers along both edges of the load rolling contactsurface is a matter of design. In other word, the endless ballcirculation path according to the present invention does not alwaysinclude the ball retainers.

Further, the die-molding material referred to in the present inventionalso includes die-casting alloys and the like besides a synthetic resinmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view (partly in section) of one embodiment of arectilinear guide unit to be manufactured by a method of the presentinvention;

FIG. 2 is a side view (partly in section) of one embodiment of thelinear guide shown in FIG. 1;

FIG. 3 is an exploded perspective view of a slider according to oneembodiment of the present invention;

FIG. 4 is a sectional view of a mobile block forming a slider shown inFIG. 3;

FIG. 5 is a perspective view of a block main body as a core of themobile block according to one embodiment of the present invention;

FIG. 6 is a front view of the block main body shown in FIG. 5;

FIG. 7 is a sectional view of the block main body when the block mainbody is inserted into a mold; and

FIG. 8 is a sectional view of the mobile block according to oneembodiment of the present invention especially when a synthetic resinmaterial is padded onto the block wherein FIG. 8(a) is a sectional viewtaken along the A--A line of FIG. 4 and FIG. 8(b) is a sectional viewtaken along the B--B line of FIG. 4.

DESCRIPTION OF REFERENCE SYMBOLS

Reference numeral 1 designates an orbital rail, reference numeral 2designates a slider; reference numeral 3 designates a ball, referencenumeral 8 designates a block main body, reference numerals 43a and 43bdesignate ball load rolling surfaces, reference numerals 44a and 44bdesignate ball return holes, reference numeral 45 designates a ballretaining section; reference numerals 50a, 50b designate chamferedsections and reference numerals 61 and 62 designate dies.

BEST MODE FOR CARRYING OUT THE INVENTION

The method of manufacture of a slider of a rectilinear guide unitaccording to the present invention will now be described by referring tothe accompanying drawings.

FIGS. 1 and 2 show one embodiment of the rectilinear guide unit in whichthe slider manufactured by the method of the present invention iscombined with an orbital rail. In these figures, reference numeral 1designates an orbital rail arranged on a stationary portion such as abed of a rectilinear guide unit, reference numeral 2 designates theslider for guiding a movable body such as a table and reference numeral3 designates balls endlessly circulating within the slider 2 whilerolling between the orbital rail 1 and the slider 2 as it bears a loadthereon.

First, the orbital rail 1 is substantially rectangular in section and atotal of four (4) lines of ball rolling contact surfaces 11a and 11b onwhich the balls 3 roll are formed along the longitudinal direction.These ball rolling contact surfaces 11a and 11b are formed on both sidesurfaces and both edges of the upper surface of the orbital rail 1,respectively, such that the ball rolling contact surface 11a is formeddownward at an angle of 30° with respect to the horizontal direction inFIG. 1 and the ball rolling contact surface 11b is formed upright.Further, the orbital rail 1 is provided with a plurality of bolt fittingholes 12 at suitable intervals in the longitudinal direction thereof sothat the orbital rail 1 is fixed to the stationary portion of themachine tool or the like by means of fixing bolts (not shown) to beinserted into these holes 12, respectively.

On the other hand, the above-mentioned slider 2 comprises a mobile block4 having a fitting surface 41 for a movable body such as a table and aplurality of tap holes 42 into which movable body fixing bolts areinserted and a pair of covers 5 which are fixed to front and rear endsurfaces of the mobile block 4 whereby when the covers 5 are fixed tothe mobile block 4, the slider can be provided therein with an endlesscirculation path for the balls 3. Further, to each of the covers 5,there is attached a seal member 6 coming into sliding contact with theorbital rail 1 so that dust and the like adhered to the orbital rail 1are prevented from entering into the slider 2 following the movement ofthe slider 2.

As shown in FIGS. 3 and 4, the mobile block 4 is substantially in theshape of a saddle having a horizontal section 4a on which the fittingsurface 41 is formed and a pair of skirts 4b drooping from thehorizontal section 4a and on the lower surface of the horizontal section4a and the inner surface of each of the skirts 4b there are formed atotal of four load rolling contact surfaces 43a and 43b, respectively.Further, on the horizontal section 4a and each of the skirts 4b, thereare provided ball return holes 44a and 44b, respectively, incorrespondence to the load rolling contact surfaces 43a and 43b so thatthe load rolling contact surfaces 43a and 43b and the ball return holes44a and 44b corresponding thereto are connected by ball change-directionpaths 51 formed in each of the covers 5 resulting in the formation of anendless circulation path for the balls 3.

With the above structure, each of the balls 3 which have borne a loadbetween the ball rolling contact surfaces 11a and 11b of the orbitalrail 1 and the load rolling contact surfaces 43a and 43b of the mobileblock 4 is released from the load when it has rolled on the load rollingcontact surfaces 43a and 43b following the movement of the slider 2, sothat the ball 3 enters the change-direction path 51 of one of the pairof the covers 5 and moves toward a direction reverse to the direction ofrolling of the ball on the load rolling contact surfaces 43a and 43b ina no-load condition so as to roll through the ball return holes 44a and44b of the mobile block 4. Further, each of the balls 3 which has rolledthrough the ball return holes 44a and 44b enters again between theorbital rail 1 and the mobile block 4 through the change-direction path51 of the other cover 5 and rolls on the load rolling contact surfaces43a and 43b while it bears a load.

Further, on both sides of each of the load rolling contact surfaces 43aand 43b there are formed ball retaining sections 45 so as to hang overthe load rolling contact surfaces 43a and 43b and when the slider 2 isremoved from the orbital rail 1, the balls 3 on the load rolling contactsurfaces 43a and 43b are prevented from falling down from the slider 2.

Further, in the instant embodiment, from the point of view of preventingas much as possible the abrasion of the balls by keeping the balls outof contact with one another within the endless ball circulation path,the balls 3 are fitted into a belt-like cage 7 made of a synthetic resinto thereby form a ball chain and such ball chain is assembled into theendless ball circulation path. For this purpose, each of the ball returnholes 44a and 44b and each of the ball retaining sections 45 areprovided with grooves for supporting both edges of the above-mentionedbelt-like cage 7 which circulates through the endless ball circulatingpath together with the balls 3.

In addition, as shown in FIG. 3, on the front and rear end surfaces ofthe mobile block 4 there are provided semicircular ball guides 46,respectively, so as to guide each of the balls 3 coming into, andgetting away from, the ball return holes 44a and 44b, side by side withthe change-direction paths 51 of the pair of covers 5.

The mobile block 4 is formed by padding a synthetic resin to themetallic block main body 8 by an injection-molding process such that theportions such as the movable body fitting surface 41 and the loadrolling contact surfaces 43a and 43b for the balls 3 where a mechanicalstrength is required are formed in the block main body 8 while theportions such as the ball return holes 44a, 44b, the ball retainingsections 45 and the ball guide sections 46 where the mechanical strengthis not deemed important are made of a synthetic resin so as to make theweight of the mobile block 4 as small as possible.

FIG. 5 is a front view of the block main body 8 before it is padded witha synthetic resin. Such block main body 8 is finished in such a mannerthat the horizontal section 4a and the skirts 4b are roughly formed bydrawing, then the movable body fitting surfaces 41, reference sidesurfaces 47 and the load rolling contact surfaces 43a and 43b are formedto have a predetermined degree of accuracy and through holes 48 asprepared holes for the ball return holes 44b are formed by drilling.Further, in the above-mentioned drawing process, in order to improve theadhesion of the synthetic resin to be padded to the block main body 8,concave portions 49 serving as resin reservoirs are formed on the outersides of the skirts 4b, respectively.

In the above case, in view of the fact that the synthetic resin ispadded around the skirts 4b of the block main body 8 at the time ofinjection molding to be performed later, substantially curved chamferedsections 50a are formed at the corners of the front and rear endsurfaces of each of the skirts 4b with the exception of the portionswhere the load rolling contact surfaces 43a and 43b are formed so thatthe molten synthetic resin at the time of injection molding is made toflow smoothly.

Next, the process of padding a synthetic resin, by injection-molding, tothe block main body 8 finished to a predetermined shape as describedabove will be explained.

This injection molding is performed by the so called insert molding inwhich the finished block main body 8 is arranged within a mold so as toact as a core whereby the synthetic resin is padded only to apredetermined portion of the block main body 8 to thereby form theabove-mentioned ball return holes 44a and 44b, the ball retainingsections 45, the ball guide sections 46 and etc.

FIG. 7 is a sectional view of the block main body 8 inserted into a moldcomprising dies 61 and 62. The die 61 has a support 63 erected thereonso as to fix the block main body 8 thereto and when the block main body8 is caused to fit about the support 63 from the direction of axis ofthe block main body 8 (i.e., the vertical direction in FIG. 7), theblock main body 8 is positioned between the dies 61 and 62 so thatcavities 64 and 65 corresponding to the ball retaining sections 45 ofthe mobile body 4 are formed between the block main body 8 and thesupport 63 and at the same time, cavities 66 for forming the ball returnholes 44a are formed between the skirts 4b and the die 61. Further, intothe through holes 48 of the block main body 8 and into the cavities 66there are inserted rod-shaped die members 67 each having a sectionalconfiguration coinciding with the shape of the ball return holes 44a and44b so that when the molten synthetic resin is filled into these throughholes 48 and the cavities 66, the ball return holes 44a and 44b areformed.

Further, the die 61 is in contact with the lower edges of the referenceside surfaces 47 of the block main body 8 whereby the molten syntheticresin to be filled into the cavities 66 is cut well to thereby preventthe synthetic resin from covering the reference side surfaces 47.

In the instant embodiment, the filling of the molten synthetic resininto the cavities 64, 65 and 66 is performed from a direction parallelto the load rolling contact surfaces 43a and 43b formed in the blockmain body 8 so that the molten synthetic resin flows quickly up to theinnermost portions of the cavities 64, 65 and 66 which extend longtoward that direction.

Thus, after the block main body 8 has been inserted between the dies 61and 62, when the molten synthetic resin is filled into the cavities 64,65 and 66 so as to be padded on the block main body 8, the mobile block4 shown in FIG. 3 is completed.

FIG. 8 is a sectional view of the mobile block 4 finished by theabove-described process especially in a state in which the mobile block4 is padded with a synthetic resin wherein FIG. 8(a) is a sectional viewof the skirt 4b when taken along the A--A line of FIG. 4 and FIG. 8(b)is a sectional view of the horizontal section 4a when taken along theB--B line of FIG. 4. As will be clear from these figures, chamferedsections 50a are formed on the front and rear end surfaces of the skirt4b of the block main body 8 and chamfered sections 50b are formed alsoat the opening edges of the through holes 48 formed in the horizontalsection 4a so that when the molten synthetic resin is filled into themold in the above-described insert-molding process, the molten syntheticresin spreads quickly around the skirts 4b and flows inside the throughholes 48.

Consequently, the equalization of thickness of the synthetic resinforming the ball return holes 44a, 44b and the ball retaining sections45 is promoted so that it is possible to prevent as much as possible thedeformation or distortion of the ball return holes 44a and 44b and theball retaining sections 45 at the time of solidification of thecontracted synthetic resin thereby increasing the dimensional accuracyof the endless ball circulation path formed by these elements. Further,it is also possible to prevent the generation of a weld line of thesynthetic resin within such endless circulation path. As a result, theslider 2 assembled by using the mobile block 4 manufactured by theabove-described process allows the balls 3 to smoothly roll within theendless ball circulation path and the slider 2 itself can smoothly moveon the orbital rail 1.

Further, since the chamfered sections 50a are formed on the front andrear end surfaces of the skirts 4b of the block main body 8,respectively, even when the synthetic resin which forms the endless ballcirculation path by being padded around each of the skirts 4b contractsafter the completion of the injection-molding process, there is nopossibility of the synthetic resin getting cracked and also due to thisadvantage, the rolling of the balls 3 in the endless ball circulationpath can be made smooth.

INDUSTRIAL APPLICABILITY

As described above, according to the method of manufacture of the sliderof the rectilinear guide unit of the present invention, even when theendless circulation path for the balls is formed by padding adie-molding material around the block main body, since the corners ofthe block main body corresponding to the endless ball circulation pathare substantially curved, the endless ball circulation path made of thedie-molding material does not crack so that it is possible to secure thesmooth endless circulation of the balls and hence the smooth movement ofthe slider.

Further, by making the corners of the block main body substantiallycurved, the molten die-molding material flows quickly around the blockmain body at the time of molding and the equalization of thickness ofthe ball return holes and the ball retaining sections forming theendless ball circulation path is promoted. Consequently, the deformationor distortion of the ball return holes or the ball retaining sections isprevented to thereby increase the dimensional accuracy of the endlessball circulation path so that it is possible to secure the smoothcirculation of the balls and hence the smooth movement of the sliderwith respect to this point, too.

What is claimed is:
 1. A method of manufacture of a slider of arectilinear guide unit, which method comprising:machining a metallicblock main body as a core of the slider to a predetermined shape havingball load rolling contact surfaces in the block main body: positioningthe block main body into a mold; and molding a body portion onto theblock main body for forming an endless ball circulation path using adie-molding material; further comprising during said machining, formingchamfered sections on front and rear edge corners of the block main bodycorresponding to a portion where the endless ball circulation path isformed during the molding, said chamfered sections being covered by thedie-molding material following the molding, whereby smooth flow of thedie-molding material occurs during the molding.
 2. The method accordingto claim 1, wherein, in said molding, a molten die-molding material isinjected from a direction parallel to the ball load rolling contactsurfaces of the block main body inserted into a mold.
 3. In a slider fora rectilinear guide unit including a metallic block main body havingball load rolling contact surfaces and a molded body portion on theblock main body for endlessly circulating balls so that an endless ballcirculation path is formed by said molding, the improvement whereinmolding-flow-smoothing chamfered sections are formed on front and rearcorners of the block main body corresponding to a portion where theendless ball circulation path is formed and are covered by said moldedbody portion.